What are Mitosis and Meiosis?
In single-celled organisms, cell reproduction gives rise to the next generation. In multicellular organisms, cell division occurs not just to produce a whole new organism but for growth and replacement of worn-out cells within the organisms.
Cell division is always highly regulated and follows a highly orchestrated series of steps. The term cytokinesis refers to the division of a cell in half, while mitosis and meiosis refer to two different forms of nuclear division.
Mitosis results in two nuclei that are identical to the original nucleus. Meiosis on the other hand results in four nuclei that each has ½ the chromosomes of the original cell. In animals, meiosis only occurs in the cells that give rise to the sex cells (gametes), i.e., the egg and the sperm.
Also Read: Cell Cycle
- Mitosis is a continuum of changes but biologists like break down the stages of mitosis into four main stages, prophase, metaphase, anaphase and telophase.
- The focus in this class is on an understanding of the process and not memorization of phases.
- The only phase name you will need to remember is metaphase.
- In mitosis the nuclear membrane is broken down, spindle fibres (microtubules) attach to the chromatids at the centromere and pull apart the chromatids.
- When the chromatids reach separate ends of the cells the spindle fibres disintegrate and a nuclear membrane rebuilds around the chromosomes making two nuclei.
- Each nucleus is identical to the original nucleus as it was in G1.
Also Read: Significance of Mitosis
- Meiosis is the form of nuclear cell division that results in daughter cells that have one half the chromosome numbers as the original cell.
- In organisms that are diploid, the end result is cells that are haploid. Each daughter cell gets one complete set of chromosomes, i.e., one of each homologous pair of chromosomes.
- In humans, this means the chromosome number is reduced from 46 to 23.
- The only cells that undergo meiosis will become sperm or eggs.
- The joining together of a sperm and egg during fertilization returns the number of the chromosomes to 46.
- Cells that undergo meiosis go through the cell cycle including the S phase so begin the process with chromosomes that consist of two chromatids just as in mitosis.
- Meiosis consists of meiosis I and meiosis II. In meiosis I homologous chromosomes are separated into different nuclei.
- This is the reduction division; chromosome number is cut in half. Meiosis II is very similar to mitosis, chromatids are separated into separate nuclei.
- As in mitosis, it is spindle fibres that “pull” the chromosomes and chromatids apart.
- The end result of meiosis is four cells, each with one complete set of chromosomes instead of two sets of chromosomes.
Also Read: Significance of Meiosis
Let us have a look at some important difference between mitosis and meiosis.
Difference Between Mitosis and Meiosis
The important difference between mitosis and meiosis are mentioned below:
|Difference between Mitosis and Meiosis|
|Interphase||Each chromosome replicates. The result is two genetically identical sister chromatids.||Interphase – Chromosomes not yet visible but DNA has been duplicated or replicated.|
|Prophase||Prophase I – crossing-over recombination – Homologous chromosomes (each consists of two sister chromatids) appear together as pairs. Tetrad is the structure that is formed. Segments of chromosomes are exchanged between non-sister chromatids at crossover points known as chiasmata (= crossing-over).||Prophase –Each of the duplicated chromosomes appears as two identical or equal sister chromatids, The mitotic spindle begins to form. Chromosomes condense and thicken.|
|Metaphase||Metaphase I Chromosomes adjust on the metaphase plate. Chromosomes are still intact and arranged as pairs of homologues.||Metaphase -The chromosomes assemble at the equator at the metaphase plate.|
|Anaphase||Anaphase I Sister chromatids stay intact. But homologous chromosomes drift to the opposite or reverse poles.||Anaphase – The spindle fibres begin to contract. This starts to pull the sister chromatids apart. At the end of anaphase, a complete set of daughter chromosomes is found each pole.|
|Mode of Reproduction||Asexual Reproduction.||Sexual Reproduction.|
|Occurs in||Eukaryotic cells.||Diploid cells.|
|Function||General growth and repair, Cell reproduction||Genetic diversity through sexual reproduction.|
|Cytokinesis||Occurs in Telophase.||Occurs in Telophase I and in Telophase II.|
|Karyokinesis||Occurs in Interphase.||Occurs in Interphase I.|
|Discovered by||Walther Flamming.||Oscar Hertwig.|
Also Read: Meiosis I
Similarities Between Meiosis And Mitosis
- Both meiosis and mitosis takes place in the cell nuclei which can be observed under a microscope
- Mitosis and meiosis, both involve cell division
- Both the processes occur in the M-phase of the cell cycle. In both cycles, the typical stages are metaphase, anaphase, telophase and prophase
- In both the cycles, synthesis of DNA takes place
- Cells of nervous tissue and the cardiac muscles tissue do not undergo the process of meiosis and mitosis once they are formed. They do not undergo division further.
The difference between Mitosis and Meiosis is quite apparent. They are two very different processes that have two different functions. Mitosis is required for genetic variation and continuity of all living organisms. Meiosis, on the other hand, is focused on cellular growth and repair of the body.
Also Read: Meiosis II
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